In this regard, isobutene is widely used for the production of a variety of industrially important products, and has been used to make methacrylic acid via methacrolein in one commercially known route. Isobutene has however been produced commercially to date through the catalytic or steam cracking of fossil feedstocks. As fossil resources are depleted and/or become more costly to use, renewable source-based routes to isobutene are increasingly needed—especially in consideration of increased demand for isobutene.
A hard-template method has previously been described for synthesizing ZnxZryOz mixed oxides for the direct and high yield conversion of ethanol (from the fermentation of carbohydrates from renewable source materials, including biomass) to isobutene, wherein ZnO was added to ZrO2 to selectively passivate zirconia's strong Lewis acidic sites and weaken Brönsted acidic sites while simultaneously introducing basicity. The objectives of the hard template method were to suppress ethanol dehydration and acetone polymerization, while enabling a surface basic site-catalyzed ethanol dehydrogenation to acetaldehyde, an acetaldehyde to acetone conversion via aldol-condensation/dehydrogenation, and a Brönsted and Lewis acidic/basic site-catalyzed acetone-to-isobutene reaction pathway.
High isobutene yields were in fact realized, but unfortunately, as later experienced by Mizuno et al. (Mizuno et al., “One-path and Selective Conversion of Ethanol to Propene on Scandium-modified Indium Oxide Catalysts”, Chem. Lett., vol. 41, pp. 892-894 (2012)) in their efforts to produce propylene from ethanol, it was found that further improvements in the catalyst's stability were needed.